1. Field of the Invention
The present invention relates to an article of manufacture and apparatus for planarizing a substrate surface.
2. Background of the Related Art
Sub-quarter micron multi-level metallization is one of the key technologies for the next generation of ultra large-scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, lines and other features. Reliable formation of these interconnect features is very important to the success of ULSI and to the continued effort to increase circuit density and quality on individual substrates and die.
In the fabrication of integrated circuits and other electronic devices, multiple layers of conducting, semiconducting, and dielectric materials are deposited on or removed from a surface of a substrate. Thin layers of conducting, semiconducting, and dielectric materials may be deposited by a number of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and electro-chemical plating (ECP).
As layers of materials are sequentially deposited and removed, the uppermost surface of the substrate may become non-planar across its surface and require planarization. Planarizing a surface, or “polishing” a surface, is a process where material is removed from the surface of the substrate to form a generally even, planar surface. Planarization is useful in removing undesired surface topography and surface defects, such as rough surfaces, agglomerated materials, crystal lattice damage, scratches, and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the features and to provide an even surface for subsequent levels of metallization and processing.
One method for polishing substrate surfaces is known as electrochemical mechanical polishing (ECMP). ECMP techniques remove conductive material and other materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion compared to conventional chemical mechanical polishing (CMP) processes. Generally, the substrate is held in a carrier head that rotates relative to a rotating platen assembly. The carrier head is adapted to controllably urge the substrate toward the platen assembly. The electrochemical dissolution is performed by applying a bias between a cathode and substrate surface to remove conductive materials from a substrate surface into a surrounding electrolyte. In one embodiment of an ECMP system, the bias is applied by polishing pad coupled to the platen. The polishing pad includes a partially conductive polishing surface that is in electrical communication with the substrate surface when the substrate is urged toward the polishing surface by the carrier head. The polishing pad also includes an electrode that functions as the cathode, and the electrochemical cell is complete when the electrolyte is flowed onto the pad.
However, hydrogen evolution, which is typically a by-product of electrochemical dissolution using acid-based electrolytes, creates challenges in the polishing process. For example, hydrogen bubble formation typically evolves at or near the electrode surface and the bubbles generally drift towards the polishing surface. Experiments have shown that the bubbles accumulating on the polishing surface create a non-uniform electrochemical reaction between the substrate surface and the polishing surface of the pad. This results in non-uniform processing results and a poor surface finish.
Another challenge is posed by the accumulation of material, such as conductive material removed from the substrate surface and reaction by products, on the electrode. This material accumulation may decrease the electrochemical efficiency and uniformity of the polishing process.
Therefore, there is a need for an improved polishing article for the removal of conductive material on a substrate surface that minimizes or eliminates the challenges discussed above.